NorthConnect
Airport Link and Northern Busway Tender Design
Preliminary Advice on Northern
Busway Pavement
HYDER SMEC JV
The assumptions used for this preliminary advice report in calculating the above Nea, HV and HVAG values are as follows:
1) In lieu of project specific Traffic Load Distributions (TLD) for buses (i.e. the
distribution of types of axle groups and the distribution of loads on each type of axle group), the Busway traffic load distribution derived from weigh-in-motion data from a bus-only lane in the ACT has been used. We understand that this TLD has been used for other Busway projects in Brisbane. 2) The number of heavy vehicle axle groups per vehicle (HVAG) is assumed to be 2.33. Based on the presumptive TLD noted above, the number of equivalent standard axles per bus (ESA/CV) is 1.1. When calculated in accordance with the Queensland Department of Main Roads “Pavement Design Manual”, the following ratios are also derived:
? the ratio of the number of standard axles of equivalent damage to the sub grade (Nes)
to the number of ESA is 1.0; ? the ratio of the number of axles of equivalent damage to asphalt (Nea) to the number of
ESA is 1.15. These estimated preliminary pavement design traffic loads may change when project traffic models and TLDs are produced. In accordance with the RFP requirements listed above, the design traffic loading in mixed used lanes (i.e., buses and other vehicles) has to be taken as the sum of the specified bus traffic and the other vehicle traffic and it has been assumed that the latter is small in comparison to the bus traffic and can be ignored for the present. This assumption should be reviewed when the traffic in mixed use lanes is identified.
1.5
Subgrade Conditions
At the present time there is little specific information available on pavement subgrade conditions throughout the study area so the following assumed subgrade design CBR values have been adopted for the purposes of preliminary pavement design; ? Road header tunnels: Bedrock floor, CBR >20%.
? Cut and cover tunnels and trough transition structures: Concrete base slab. ? Natural soils at grade or less than 1m of embankment fill: CBR 3%.
It is assumed that in road header tunnels with a bedrock subgrade, a 300mm thick drainage blanket overlain by geotextile will be constructed beneath the pavement to control groundwater seepage.
In accordance with technical standard PSTS101 “Checking Sub grade: Capping layer; Drainage Layer; Controlled Subgrade; Working Platform; Temporary Pavement; Verge”, where the subgrade has a design CBR less than 3% a capping layer will be required. It is anticipated that for some natural soils the subgrade materials may have to be excavated and replaced with imported materials to form the capping layer; for example a soil with design CBR 2% requires capping 200mm thick. Pavements with capping are designed as having a design CBR value of 3% at the top of the capping layer.
In addition, where the natural soils have a swell (in the CBR test) of greater than 0.5% a controlled subgrade is required with minimum thickness depending on the swell value. For example, for a design swell value greater than or equal to 2.5% and less than 5%, the
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NorthConnect
Airport Link and Northern Busway Tender Design
Preliminary Advice on Northern
Busway Pavement
HYDER SMEC JV
required thickness of the controlled sub grade is 600mm. The working platform (see Section 6) forms part of the controlled sub grade.
1.6
Preliminary Busway Pavement Assessment / Design ( No LRT ): Rigid Pavement Design Review
The RFP specifies that rigid pavements are to be used in the Busway at the following locations;
? Tunnels and Connection ramps.
? Busway Stations including through lanes, standing lanes and tapered approaches. ? Bus turnaround area at Kedron. ? Federation Street bus stop. ? Bus stops.
The RFP designs have been assessed in accordance with the QDMR design manual and are presented in Tables 1, 2 and 3 following together with our recommended design amendments (highlighted in bold) required for design life and anticipated sub grade conditions. In all cases the minimum pavement thickness nominated in the RFP is satisfactory for the nominated bus traffic loading provided that shoulders are provided as discussed below.
Additional design parameters used in accordance with the RFP and QDMR rigid pavement requirements are as follows; ? Project design reliability = 97.5%
? JRCP dowelled and CRCP pavements, for which the required Load Safety Factor =
1.25 ? Rigid pavements will be provided with shoulders as follows;
?
A shoulder made up of the same concrete and thickness as the trafficked lane base concrete thickness, cast integrally with the trafficked lane concrete base and with a minimum width of 0.6m outside the edge line; or
A shoulder made up of the same concrete and same thickness as the trafficked lane base concrete thickness, cast separately to the trafficked lane concrete base and keyed and tied to the base, with a minimum width of 1.5m outside the edge line.
?
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NorthConnect
Airport Link and Northern Busway Tender Design
Preliminary Advice on Northern
Busway Pavement
HYDER SMEC JV
Table 1: RFP Busway Pavement Design (No LRT) – Rigid Pavement: Tunnels and
Connection Ramps Layer Thickness (mm) 45 Material Asphalt surfacing CRCP Concrete Base Concrete Sub base Working platform
DG14 Asphalt 240 4.5 MPa characteristic flexural strength 150 Lean mix concrete (PSTS39 Aug 06 to apply) 150mm Unbound granular material (modified and with surface seal in accordance with PSTS101 Aug 06) The actual sub base type in tunnels and ramps will depend on supporting materials, drainage requirements and construction practices and may vary from that shown above. In particular, while not strictly conforming to PSTS39, it is likely that the lean mix concrete sub base will be replaced by no fines concrete where rock is exposed in the floor of the road header tunnel.
Table 2: RFP Busway Pavement Design (No LRT) – Rigid Pavement: Busway
Stations, Kedron Turnaround and Federation Street Bus Stop. Layer Thickness (mm) 240 Material CRCP Concrete Base Asphalt Seal Concrete Sub base Working platform Controlled subgrade 4.5 MPa characteristic flexural strength with dark oxide finish consistent with urban design 30 DG10 Asphalt 150 Lean mix concrete (PSTS39 Aug 06 to apply) 150 Unbound granular material (modified and with surface seal in accordance with PSTS101 Aug 06) Varies See section 1.5 (typically150-300mm)
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NorthConnect
Airport Link and Northern Busway Tender Design
Preliminary Advice on Northern
Busway Pavement
HYDER SMEC JV
All CRCP concrete bases will have longitudinal and transverse reinforcement. Longitudinal reinforcement should comprise 16mm diameter deformed reinforcing bars spaced at 110mm centres. The amount of transverse reinforcement within the base slab and across longitudinal joints will depend on the location of longitudinal joints, whether barriers will sit on the pavement slab and whether provision for the LRT is required and further advice will be provided when these details are known.
Table 3: RFP Busway Pavement Design (No LRT) – Rigid Pavement: Bus Stops. Layer Thickness (mm) 240 Material JRCP Concrete Base Concrete Sub base Working platform Controlled subgrade
4.5 MPa characteristic flexural strength with dark oxide finish consistent with urban design 150 Lean mix concrete (PSTS39 Aug 06 to apply) 150 Unbound granular material (modified and with surface seal in accordance with PSTS101 Aug 06) See section 1.5 Varies (typically150-300mm) Slab reinforcement will typically comprise F82 mesh (subject to slab length). Transverse joints between slabs will be dowelled with 32mm diameter plain round bars 450mm long at 300mm centres. The amount of transverse reinforcement across longitudinal joints will depend on the location of longitudinal joints, whether barriers will sit on the pavement slab and whether provision for the LRT is required and further advice will be provided when these details are known.
1.7
Preliminary Busway Pavement Assessment / Design ( No LRT ): Flexible Pavement Design Review
The RFP specifies that a granular pavement with an asphalt base and wearing course is to be used at the following locations; ? Busway lanes ? Bus-only lanes ? Turo Street Bus lane
The RFP specifies a flexible granular pavement design, which is presented in Table 4 overleaf together with our preliminary recommended design amendments (highlighted in bold) required for design life and anticipated subgrade conditions. The pavement design has been carried out using extrapolation of the design charts in the Austroads Pavement Design Manual and a mechanistic design will be carried out to confirm thickness requirements.
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NorthConnect
Airport Link and Northern Busway Tender Design
Preliminary Advice on Northern
Busway Pavement
HYDER SMEC JV
Table 4: RFP Busway Pavement Design (No LRT)– Flexible Pavement: Bus Lanes
(assumed subgrade CBR 3%) Layer Thickness (mm) 40 Material Asphalt wearing course Seal Asphalt base layer OGA 14 asphalt -- Not specified (nominal 50mm) Not specified (620mm total thickness) 150 Not specified (PMB seal with 10mm cover aggregate) Not specified DGA 14 with A15E binder Granular base Type 2 subtype 2.1 unbound granular base materials over Type 2 subtype 2.3 unbound granular sub base materials Not specified (assumed to be Type 2 subtype 2.5 unbound granular material) Required where sub grade is CBR <3%, See section 2 Working platform Capping materials
Varies It is expected that the above granular pavement will require significant maintenance works throughout its 40 year design life and is not recommended due to the potential for early distress. As an alternative, consideration should be give to the use of a Full Depth Asphalt (FDA) pavement instead. For comparison we have prepared a preliminary design profile for such a pavement as presented in Table 5 overleaf.
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